1. Field of the Invention
The present invention relates to an optical writing control apparatus, an image forming apparatus, and an optical writing control method, and in particular, to a technology for controlling a detection timing to detect a drawn image.
2. Description of the Related Art
In recent years, more and more information is made into electronic forms, and image processing apparatuses, such as a printer and a facsimile machine used to output electronic information and a scanner used to electronic documents, have been playing an essential role. Such an image processing apparatus is often configured as a multifunction peripheral (MFP) that has an imaging function, an image forming function, and a communication function so as to be used as a printer, a facsimile machine, a scanner, and a copier.
Among the image processing apparatuses as described above, an electrophotographic image forming apparatus is widely used as an image forming apparatus for outputting electronic documents. The electrophotographic image forming apparatus forms an electrostatic latent image by exposing a photoreceptor, develops the electrostatic latent image with a developer, such as toner, to form a toner image, transfers the toner image to a sheet of paper, and outputs the sheet of paper.
In the electrophotographic image forming apparatus as described above, a timing at which the electrostatic latent image is drawn by exposure of the photoreceptor and a conveying timing of the sheet of paper are synchronized so that the image can be formed in a correct area of the sheet of paper. Furthermore, in a tandem-type image forming apparatus that forms a color image by using a plurality of photoreceptors, an exposing timing of each of the photoreceptors for different colors is adjusted so that images developed on the photoreceptors of the colors can accurately be superimposed one on top of the other (see, for example, Japanese Patent Application Laid-open No. 2004-191459). In the following, the above-described adjustment processes are collectively referred to as positional deviation correction.
As a concrete example of a method to implement the positional deviation correction as described above, a mechanical adjustment method is known, in which a positional relationship between a photoreceptor and a light source that exposes the photoreceptor is adjusted. Furthermore, a method using image processing is also known, in which an image to be output is adjusted according to a positional deviation so that the image can be formed at a preferable position in an end product. In the method using the image processing, the image to be output is shifted in the sub-scanning direction so that the image can be formed at a desired position.
The electrophotographic image forming apparatus also performs, in addition to the positional deviation correction, density correction in which an adjustment value is obtained to adjust the intensity of light used to adjust the photoreceptor or to adjust a developing bias for developing an electrostatic latent image so that a desired density can be obtained in an image to be output.
In the correction operation as described above, it is necessary to draw and read a correction pattern, so that toner is consumed. Therefore, to reduce the toner consumption, there is a need to draw the correction pattern as small as possible. Incidentally, when a density correction pattern is to be read, if the spot of light from a sensor that reads the pattern is applied across a pattern drawing area and a background area, a density detection error occurs. Therefore, it is necessary to drive the sensor while the pattern drawn and conveyed is covering a detection position of the sensor.
To draw the density correction pattern in a smaller size and to drive the sensor while the pattern is covering the detection position of the sensor as described above, it is necessary to synchronize a timing at which the pattern is drawn and conveyed to the detection position of the sensor and a drive timing of the sensor. However, in the electrophotographic image forming apparatus including various mechanisms, such as an image forming mechanism provided with an optical writing device and a photosensitive drum or a conveying mechanism such as a belt for conveying a developed image, it is difficult to synchronize the timings with high accuracy.
Therefore, there is a need for an electrophotographic image forming apparatus capable of performing the positional deviation correction in the sub-scanning direction with high accuracy while reducing a drawing area of the density correction pattern.